Melanoma has been one ofthe fastest rising malignancies in the last four decades with cases increasing from below three per 100,000 people to above 13 (18.9 if only whites are counted). The following discoveries have been made that serve as the basis for this program project: 1) Mutations in genes ofthe MAP kinase pathway are frequent in melanoma and mutually exclusive. Mutations are most frequent in BRAF (50%) followed by NRAS (15%) and c-kit (4%). 2) Within each mutation group there are sub-groups due to additional critical mutations. 3) The biological characteristics of melanomas including their progression and metastasis are driven by both tumor and microenvironment forces. 4) Small molecule inhibitors for tumor-associated kinases lead to powerful effects on melanoma cells both in vitro and in vivo. Our first objective is to identify somatic alterations in growth factor mediated signaling pathways and determine whether they are targets for therapy. Our group (Project 2, Bastian) has recently identified c-kit mutations in melanoma, particularly in acral and mucosal melanomas, that are mutually exclusive to BRAF and NRAS mutations, and emerging trial data suggest that drugs targeting c-kit induce significant clinical responses in some patients with these mutations. Several lines of evidence point towards a wider role ofthe c-kit signaling pathway is specific types of melanoma and we will perform detailed genetic and functional analyses to analyze the pathway for additional therapeutic targets and factors of primary and secondary resistance to ckit directed therapies (Project 2, Bastian). Two other genes that function downstream of c-kit encoding isoforms of the p70S6 kinase, critical regulators of protein synthesis and cell growth, are also amplified in many melanomas. Therefore, we will characterize the biochemical properties of p70S6K and develop potent and specific inhibitors to this kinase (Project 3, Marmorstein). Our complementary second objective that focuses on therapy resistance in melanoma is to identify sub-populations of tumor cells that are drivers for tumor progression and evaluate combination therapeutic strategies that target this tumor cell sub-population in addition to the bulk of tumor cells. Our group (Project 1, Herlyn) has identified melanoma cells with high self-renewing capacity that are very slowly cycling but have a high proliferative reserve. They are characterized by expression ofthe histone 3 K4 demethylase JARID1B. In this proposal we will characterize the signaling mechanisms mediating therapy resistance in JARID1B+ cells and biochemically analyze the JARID1B protein to develop and evaluate therapeutic strategies using inhibitors to JARID1B and/or JARIDIB-dependant signaling (Project 3, Marmorstein and Project 1, Herlyn).